In manufacturing precision circuits for use in highly sophisticated equipment such as computers and the like, wafers or substrates form the base material for such printed circuitry and may be made of silicone, glass, ceramic materials of various sorts, and other similar materials in very thin wafer-like form. As a part of the processing of such substrates or wafers, it is desirable in various processing steps, to accomplish etching of certain areas of the substrate, to remove photoresist coating which may be applied to the substrate to limit the areas of etching, or to otherwise clean the substrate. In all of these processing steps, the use of an acid is required.
It will be understood, however, that after the completion of such stripping, etching or cleaning processes, the substrates must be extremely clean, without the smallest traces of acid remaining on the substrate.
Where herein, reference is made to etching or stripping processes, it should be considered that reference is also being made to all of the other similar processing of substrates using acid and other similar solutions.
In processing such substrates which may be coated with photoresist, the substrates are supported at their edges in spaced relation from each other in a carrier or basket, and it has been common practice in the past to mount a number of such baskets on a rotary turntable arranged so that the substrates lie substantially perpendicular to the axis of the turntable and the substrates revolve with the carrier and the turntable around the axis. The turntable is confined within a bowl made of stainless steel or other acid resisting material and having a top through which access is obtained into the bowl. The top of the bowl or may not be entirely tiltable upwardly off the bowl to form a closure, but in the event the top of the bowl is stationary, an access port and cover will be provided allowing access into the bowl to place and retrieve the baskets of substrates on the turntable.
In order to apply the acid and rinsing water (oftentimes deionized water) to the substrates, it has been common practice in the past to locate a manifold type post extending downwardly from the top of the bowl approximately at the axis of the turntable with laterally directed nozzles to alternately spray acid and rinsing water and to also carry air or gaseous nitrogen under high pressure and velocity to atomize the acid into a fog type spray for application to the substrate. Application of rinse water from the centrally located manifold post and nozzles has proved to be entirely inadequate because cleaning of the bowl and the turntable in this manner is incomplete and not completely possible. The result has been that the substrates are not entirely free, to the extent necessary, of acid after completion of the cycle of operation in the bowl. It has been found that, if any trace or minute particles of acid remain on any of the surfaces within the bowl, the substrates cannot be expected to be reliably free of acid particles to the degree required by further processing of these substrates.